Purification of naphthene hydrocarbons



Patented Aug. 30, 1949 PURIFICATION OF NAPHTHENE HYDRO CARBONS Alfred E. Hirschler, Drexel Hill, Pa., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey No Drawing. Application May 27, 1946, Serial No. 672,685

6 Claims. (01. 260-666) 1 This invention relates to the separation of hydrocarbons and is particularly directed to a method of preparing a naphthene hydrocarbon of relatively high purity from a mixture comprising the same together with one or more parafiin hydrocarbons.

In the preparation of individual hydrocarbons by organic synthesis, it is seldom that the desired hydrocarbon may be produced directly in a high state of purity. Generally a mixture of hydrocarbons is formed, which includes compounds which may boil relatively close to the desired hydrocarbon. A usual procedure of purification involves distillation under fractionating conditions whereby removal of compounds having boiling points sufiiciently different from that of the desired hydrocarbon may be accomplished.

It is often the case, however, that a high degree of purity may not be attained in this manner, or may be obtained only with great difliculty, due

:to the proximity of boiling points of the 'various compounds. Likewise, in the separation of a particular hydrocarbon from a complex hydrocarbon mixture such as petroleum or coal tar fractions, it is often extremely difficult to segregate the desired component as a product of high purity due to the presence of other compounds of close boiling points. While the use along with straight distillation of other procedures, such as solvent extraction and azeotropic distillation, has resulted in improved separations in certain cases, generally speaking it has not been practical heretofore to produce hydrocarbons of high purity from mixtures containin closely related hydrocarbons. ,Usually the best that has been done from a practaining close boiling compounds heretofore has been extremely difficult and, in many cases, practically impossible.

The present invention provides an improved method whereby relatively pure hydrocarbons of the naphthenic class may be prepared from a starting material comprising the desired naphthene, preferably in predominant amount, together with one or more paraffin hydrocarbons.

.The method is particularly useful where the components in the starting mixture boil closely togather, as where they have the same number of, or difier by not more than one or two, carbon atoms per molecule. The purification is accomplished according to the invention by selective 2 adsorption of the paraflin from the naphthene, utilizing activated carbon as the adsorbent.

The removal of a paraffin hydrocarbon from a naphthene by selective adsorption of the paraflin on activated carbon, so as to obtain the naphthene in a relatively high state of purity, does not appear to have been accomplished heretofore. I have found that activated carbon is capable of removing the paraflinic component from some mixtures of this type regardless of the concentration of the parafiin in the mixture. This is particularly true where the paraflin is a straight chain compound. For example, n-hexane-cyclohexane. n-heptane-methylcyclohexane, and n-octane-ethylcyclohexane are mixtures from which activated carbon will selectively remove the parafiln substantially regardless of the proportion of paraffin in the mixture.

I have further found that there ar many other paraiiin-naphthene mixtures from which activated carbon will not selectively adsorb the paraiiin when present in large proportion. but will, however, selectively remove the paraflin when its proportion is not too great in the mixture.

Paraffins which are branched chain, but not too highly so, tend to form this type of mixture. When the behavior is of this type, the naphthene may be purified by starting with a mixture containing the paraflinic component in a proportion substantially less than that at which the naphthene is selectively adsorbable and then treating such mixture with activated carbon. Preferably, the starting mixture should contain a predominant amount of the naphthene and only a minor amount of the paraffin. The smaller the amount of the parafiin the more easily its removal may be effected. This is in contrast to other separation methods such as distillation or solvent extraction wherein the separation becomes more diiiicult as the amount of a component decreases.

There are-still other paraffin-naphthene mixtures from which activated carbon is incapable of selectively adsorbing the parafiin even when it is present in low concentration. The tendency is toward this type of behavior when the parafiinic component is a highly branched chain compound. An example of this type of mixture is 2,2,4-trimethylpentane-methylcyclohexane, wherein the naphthene is the more strongly adsorbable component throughout the whole concentration range. On the other hand, 2,2,3-trlmethylbutane is adsorbable on activated carbon from a mixture of the same with cyclohexane provided the 2,2,3- trimethylbutane content is below about 20-25%. This shows that the fact that a parafiin has a highly branched chain does not necessarily mean that it will not be removable from a naphthene with which it is associated.

It has not been possible thus far to predict with absolute certainty just which type of behavior will be :encountered forganyi iven combination of a parafiin and a naphthene: Inorder to be certain that the present method. is appli-, cable for any given mixture, it is best to pre determine that the paraffin actuallvwill be s tively adsorbable at the concentration at whichiit occurs in the starting miXture.

In practicing the invention,,a.'.chargematerial is selected which contains the parafiinic component in a proportion at which it is selectively adsorbable. Preferably the charge shouid con tain a large amount of the desired naphthene and only a small amount (say 20% or,;less .of: the parafiin as impurity. This mixture is then treatedcwith -,activatedf;carbon to. seleetixe w sorb theparafliniecomponent. In order "to e e'ct a,high1 degree or separation; the treatment isiicarried but ,preferably, by; percolating j the charge th'rougha column ,of the 1 adsorbent while em playing, a. large, proportion. of the? adsorbent. After;all".of, ',the charge has passed; into" the actsorbent,, it maybe followedeby a desorbing agent comprising .a ,materialfmore stron ly adsorbable by activated carb'ontthan the .adsor-bate in order I to.,effct displacement of, thecharge material fr'fom,,the adsorbentgi, Examples :of: suitable de= sorbing agents. are benzene, toluene, xylene, phenol .or. other I aryl lcompounds A relatively 16w boiling. aliphatic hydrocarbon such as "butane or. ,pentane alsolmay. be employed .as ithedesorbing lagent; -,par ticularly: whe the. charge material is"sufliciently ,highiboiling to be greadily separable therefrom distillation; I A., desorbin agentjsfnot requiredghowever; if sufllcienticharge isgusedi to ,wet alllofl the adsorbent'andfprocluce" a-Mfiltrate, The vfirst,,pprtion Lofjefllux or. filtrate from thecolumn. will', comp'ris'ethe naphthene in a. relativ.ely highstateoipurity; as compared to the charge. S ucceedi'ng portions'willdecrease in .pnrity and;l,as the adsorb ate is displacedfrom thee-gel ,the. fi1trate willfbecome less pure than the charge. Thetfiltrate irom. tll'B'COlllHlll may be cut. ,into. fractions as. desired .in' order: to segregate theportion containing the 'naphthene in the. puritytdesired...

The fo1lowing, .example s,' in which" percentages are hy.volume.,.will serveto illustrate'more specifically how. the inventionimay be practiced,

Ezrample' 'lv A column'havingan internal diameter of about A inch andaheight of 3 feet was-packed with 50 grams -of '60-'90 mesh activatedcarbon: The column was provided with a-" water jacket "through which water wascontinuously 'circulat'edat a temperature of about 45550? to absorb' heat generatedgdue to wettingofjthe adsorbenti Sixty milliliters of astarting mixture consisting of 90% methylcyclohexane and %"n-'heptan'e were percolated' downthrough'tlie columnz After all of theicharge had passedinto the adsorbent, it'was followed byb'enzene to displace the charge material fromjthercolumn'; The filtrate was collected infractions' and the composition of each fraction was determined. 'Il'ie:first'- fraction amounting to- 22%,of the charge was substantially100%' pure methylcyclohexane: The next'fraction (22 3'8% oficharge) was 97.5%"pure; About50% of the total filtrate containedmethylcyclohexane in a concentration higher than that-of the charge:

Example II In this example a mixture consisting of 90% cyclohexane and 10% 2,2,3-trimethylbutane was treated in the same manner as described in Examplel-Ilexceptthat 49.mil1i1i t,ers,of charge were used; Twoq10% tractionsof filtrate'were obtained and were found to contain respectively 93% and 91.5% cyclohexane. Further purification could have beenefiected by retreating the fractions with activated carbon.

Example III Aimixtureponsisting of 90% ethylcyclohexane and110%jn7:-,0ctane was treated in the manner de- 5 scribed in Example I except that 49 milliliters of chargevwereeused. The first cut amounting to 201 of the change was substantially 100% pure ethylcyclohexane. The second cut (-41% of charge) was 96% pure. A total of about 73% was 20 obtained with an ethylcyclohexane content higher thanthat offth'e charger Ewample II/s Forty ninemilliliters of a mixture ccnsisting of- 9235.%"' cyclohexane and 'l l5 n-h exane :were

treated in the manner previously describedn The In -=practicingthe-invention it generallyzwill be 0 desirable to reactivate the adsorbent after it has fbeen used in order that-it may be used iagain.

This may -be--done by blowing the adsorbent'zwith hot iner-t gas or -air -to"drive:off the adsorbedzhydrocarbons or "to drive off thexdesorbing agent if 5 -one has' been 'used.

The temperature at which the adsorption operation is car-ried out may afiect the efliciency of fthe separation' and itofterr-will be the-:case that a poorerseparation willbe 'obtained'at :ele-

4U vated' temperature: The operation-thereforesis preferably conducted at room 1 temperature or below to-'-insureea betterseparation. Thiss general-lywillneeessitate the provision of some means for'removing any heat generated due to wettin 5-of the-adsorbent as; for instance, by providing means for circulating a-: cooling medium around the i adsorbent-1 column.

In my copending applicatiomSerial-No. 643;764, file'cl' January 26f1946} now U; S": Patent' No.

21464931, thereis described and claimed a method for remQVin parafiin hydrocarbons from naphth'enes-wherein the adsorbent is silicagel or other adsorbent 4 substantiall'y conforming to siiica'gel'in adsorptive properties: The activated 'carb'onused according to the present methodis an-adsorbent-of a different type and generally would n0t-be-considered" as having properties substantially equivalent to thoseof silica gel. Aetivated" carbonis organophilic whereas adsorbents such as-silica gel are hydrophilic. Accordingly, in- -many cases activated carbon'exhibi-ts adsorptiveproperties sub'stantially different from those of silica gel; and-in fact, for many hydrocarbonsystems the activated carbon gives substantially improved results.

various "modifications of the herein described processarepermissible within the broad aspects of the invention and will be apparent to'those skilledin'th'e art.

Having described-myinvention, what I claim and-desireto protect-by Letters Patent is:

1. A process'for purifying anaphthene hydrocarbon froma non-aromatic liquid mixture composedof amajor'amount of said naphthene hydrocarbon" and aminor amount of a: straight chain parafiin hydrocarbon which comprises filtering the mixture through a body of activated carbon, thereby selectively adsorbing said paraffin hydrocarbon, and separating from the adsorbent a filtrate fraction containing the naphthene hydrocarbon in more nearly pure form.

2. A process according to claim 1, wherein the said hydrocarbons differ by not more than two carbon atoms per molecule.

3. A process according to claim 1 wherein the said hydrocarbons contain the same number of carbon atoms per molecule.

4. A process for purifying a naphthene hydrocarbon from a non-aromatic liquid mixture composed of a major proportion of said naphthene hydrocarbon and a minor proportion of a paraffin hydrocarbon, said major proportion of the naphthene being in excess of any proportion at which the naphthene is selectively adsorbable, which comprises filtering the mixture through a body of activated carbon, thereby selectively adsorbing said parafifin hydrocarbon, and separating from the adsorbent a filtrate fraction containing the naphthene hydrocarbon in more nearly pure form.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,415,315 Walter et al. Feb. 4, 1947 2,425,535 Hibshman Aug. 12, 1947 OTHER REFERENCES Cawley, Jour. Soc. Chem. Ind., vol. 60, 205-7 (1941).

Mair et al., The Oil and Gas Journal, September 19, 1935, pages 29, 30, 32.

Mair et al., Jour. Res. Nat. Bur. Stand, vol. 32, 165-183 (1944). 

